Radio communication system

ABSTRACT

In a radio communication system a first radio station performs communication by the use of a first radio signal. A second radio station receives a second radio signal which is indistinguishable from the first radio signal. A third radio station is in a radio communication area of the first radio station and a radio communication area of the second radio station. A communication format conversion unit generates a third radio signal by converting a communication format of the second radio signal to a communication format which is distinguishable from the first radio signal, and communicates with the third radio station by the use of the third radio signal.

This is a continuation of International Application No.PCT/JP2009/050775, filed Jan. 20, 2009, now pending, the contents ofwhich are herein wholly incorporated by reference.

FIELD

The embodiments discussed herein are related to radio communicationsystems including a mobile telecommunication system, a radio LAN (LocalArea Network) and the like.

BACKGROUND

In recent years a new high-speed communication service referred to asLTE (Long Term Evolution) has been expected as a standard forcommunication by a mobile station such as a portable telephone. Inaddition, a LTE-advanced system which is a further developed version ofLTE is discussed in 3GPP (3rd Generation Partnership Project).

Furthermore, the LTE-advanced system is to be proposed as anIMT-advanced system which is a further developed version of an IMT(International Mobile Telecommunication)-2000 system which ITU-R(International Telecommunication Union Radio communications sector)determines to discuss.

W-CDMA (Wideband-Code Division Multiple Access), CDMA one, and WiMax(Worldwide Interoperability for Microwave Access) are typical IMT-2000systems.

With a LTE-advanced system introducing a MBSFN (Multimedia Broadcastmulticast service Single Frequency Network) in which MBMS (MultimediaBroadcast Multicast Service) data is transmitted and a relay apparatus(relay node) for performing radio relay with a LTE system as a base isdiscussed (expansion of uplink/downlink bandwidth, introduction ofuplink MIMO (Multiple Input Multiple Output), and the like are alsodiscussed). Description will now be given with a LTE-advanced system asan example.

(1) MBMS and MBSFN

A MBMS is a service for broadcasting data to unspecified or specificusers. To be concrete, broadcasting information such as news ormulticasting information to specific users is possible.

Furthermore, A MBSFN in which a plurality of base stations transmit MBMSdata in synchronization with one another by the use of the same resourceis discussed as a method for transmitting broadcast data (MBMS data) bythe use of a MBMS.

“SFN” (Single Frequency Network) of “MBSFN” means using the same radiofrequency. That is to say, usually a transmission area (MBSFN are) isset in a MBSFN and the same radio frequency is used in that area (seeTS36.300V8.6.0 15 MBMS).

Moreover, with a MBSFN a plurality of base stations transmit the samedata at the same frequency at the same timing. As a result, a mobilestation can receive MBMS data transmitted from the plurality of basestations.

The reason for this is as follows. If delay time is shorter than orequal to the length of a CP (Cyclic Prefix) in, for example, OFDM(Orthogonal Frequency Division Multiplexing) receiving, then pluralpieces of data can be received and synthesized. By receiving andsynthesizing plural pieces of data, the effect of the improvement of areceiving characteristic can be obtained.

A CP is a redundant portion added at data transmission time to prevent adata overlap, and corresponds to a GI (Guard Interval) in terrestrialdigital broadcasting. The length of a CP used in a MBSFN is longer thanthat of a CP added to unicast data in normal communication.

FIG. 20 illustrates the format of radio data. Radio data includes a CPand data. A CP used at unicast transmission time is referred to as anormal CP and a CP used in a MBSFN is referred to as an extended CP. Thelength of a normal CP is 4.69 μsec and the length of a CP used in aMBSFN (length of a CP included in MBMS data) is 16.67 μsec.

FIG. 21 illustrates data receiving and combining. It is assumed that amobile station 120 receives MBMS data (data b) transmitted from a basestation B and that the mobile station 120 receives MBMS data (data a)transmitted from a base station A time t after receiving the data b(data a and b are broadcast data and are equal in service contents).

If the delay time t falls within the range of the length of a CP fromthe time when the mobile station 120 begins to receive the data b, thenthe mobile station 120 can receive not only the data b but also the dataa and combine the data a and b. As described above, a CP is long in aMBSFN. Therefore, a mobile station can also receive MBMS datatransmitted from a remote base station (corresponding to the basestation A in this example) and can perform combining.

(2) Relay Apparatus (Relay Node)

With a LTE-advanced system a relay node is installed between a basestation and a mobile station, for example, for cell extension or ascountermeasures for dead spots.

FIG. 22 illustrates cell extension. A mobile station 120 is outside acell 100 a of a base station 100. A relay node 110 is installed withinthe cell 100 a. The mobile station 120 is within a relay area 110 a inwhich the relay node 110 can perform relay.

If a relay node such as the relay node 110 does not exist, the mobilestation 120 is outside the cell 100 a and cannot communicate with thebase station 100. However, if the relay node 110 is installed, themobile station 120 is within the relay area 110 a of the relay node 110.Even if the mobile station 120 is outside the cell 100 a, radio relay isperformed via the relay node 110 and communication can be performedbetween the base station 100 and the mobile station 120.

FIG. 23 illustrates countermeasures for a dead spot. A relay node 110 isinstalled within a cell 100 a of a base station 100. There is a deadspot 110 b within the cell 100 a. A mobile station 120 is in the deadspot 110 b. It is assumed that a relay area 110 a of the relay node 110covers the dead spot 110 b.

If a relay node such as the relay node 110 does not exist and the mobilestation 120 is in the dead spot 110 b, it is difficult for the mobilestation 120 to communicate with the base station 100. However, if therelay node 110 is installed and the relay area 110 a of the relay node110 covers the dead spot 110 b, then radio relay is performed via therelay node 110 and communication can be performed between the basestation 100 and the mobile station 120 in the dead spot 110 b.

The following technique is proposed in Japanese Laid-open PatentPublication No. 2008-503130 (Paragraphs [0015]-[0020], FIG. 1) as aconventional technique regarding a MBMS. A mobile station estimates cellquality on the basis of the difference in transmission power between acommon pilot channel and a common control channel and receives data froman adjacent cell in which cell quality is the highest.

In addition, the following technique is proposed in Japanese Laid-openPatent Publication No. 10-032557 (Paragraphs [0019]-[0021], FIG. 1) as aconventional radio relay technique. A transmission apparatushierarchizes and transmits a relay apparatus signal which a relayapparatus retransmits and a receiving apparatus signal transmitteddirectly to a receiving apparatus. The relay apparatus demodulates therelay apparatus signal, modulates it again, and retransmits it.

With a MBMS radio network, as described above, a relay node can beinstalled for performing cell extension or taking countermeasures for adead spot. In addition, with a MBSFN a radio signal is transmitted bythe use of an extended CP which is longer than a normal CP used fornormal unicast transmission. Accordingly, a radio signal transmittedfrom a base station distant from a mobile station can be received via arelay node. As a result, the possibility of receiving and combining morepieces of data can be enhanced.

With a conventional MBMS radio network, however, the problem of beingunable to distinguish between unicast data and MBMS data transmitted ina MBSFN exists.

FIG. 24 illustrates the problem of being unable to distinguish betweenunicast data and MBMS data. There are base stations 101 through 103,mobile stations 121 through 123, and a relay node 110. The base station101 transmits unicast data r1 to the mobile station 121. The basestation 103 transmits unicast data r3 to the mobile station 123. Inaddition, the base station 102 transmits MBMS data r2 to the relay node110 and the relay node 110 relay-transmits the MBMS data r2 to themobile station 122.

With unicast data transmission the base station scrambles unicast dataso that the unicast data can be distinguished from another piece ofunicast data transmitted by the use of the same radio resource. That isto say, by using scrambling codes which differ in initial value, theunicast data can be distinguished from another piece of unicast datatransmitted by the use of the same radio resource. Accordingly, theunicast data r1 and r3 indicated in FIG. 24 can be distinguished. Inaddition, with MBSFN transmission plural pieces of MBMS data aretransmitted so that they can be distinguished. Therefore, pieces of MBMSdata can be distinguished. That is to say, if the same communicationformat is used, pieces of data can be distinguished.

However, unicast data and MBMS data differ in communication format. Inaddition, there is no express provision that unicast data and MBMS datadiffer in scrambling code initial value. Accordingly, there is noguarantee that unicast data and MBMS data can be distinguished byscrambling codes. Furthermore, unicast data and MBMS data may betransmitted at the same time by the use of the same radio resource. As aresult, in an environment in which unicast data and MBMS data mingle, itmay be impossible to distinguish between them.

To be concrete, there is no guarantee that a scrambling code for a PDSCH(Physical Downlink Shared Channel), which is a radio channel used fortransmitting user data in unicast communication, and a scrambling codefor a PMCH (Physical Multicast Channel), which is a radio channel usedfor transmitting user data in MBSFN transmission can be distinguished.As a result, it may be impossible to distinguish between a PDSCH and aPMCH. This may cause interference.

In the case of FIG. 24, it is assumed that the mobile station 121 is ata position where the mobile station 121 can receive both the unicastdata r1 and the MBMS data r2 and that the mobile station 123 is at aposition where the mobile station 123 can receive both the unicast datar3 and the MBMS data r2.

In this environment, the mobile station 121 or 123 which originallywants to receive unicast data is unable to distinguish MBMS data r2transmitted from the relay node 110, so that the MBMS data r2 becomes aninterference wave.

On the other hand, even if unicast data and MBMS data can bedistinguished for a certain period of time, base stations or a basestation and a relay node are not necessarily synchronized. Accordingly,timing at which scrambling begins, for example, in one base stationgradually deviates from timing at which scrambling begins in the otherbase station. This degrades code identification capability. As a result,it is impossible to distinguish a PDSCH and a PMCH, and interferenceoccurs.

FIG. 25 illustrates the occurrence of interference caused by a timingdeviation. A black slot indicates MBMS data in MBSFN transmission and awhite slot indicates unicast data. In a state in which transmissionsequences A1 and B1 can be distinguished, two pieces of MBMS data are inthe same timing, for example, at a timing T1. Accordingly, the twopieces of MBMS data can be distinguished and interference does notoccur. Two pieces of unicast data are in the same timing at a timing T2.Accordingly, the two pieces of unicast data can be distinguished andinterference does not occur.

On the other hand, it is assumed that the transmission sequence A1changes to a transmission sequence Ala due to a timing deviation. Inthis case, MBMS data and unicast data are in the same timing in thetransmission sequences Ala and B1 at each of timings T3 through T6.Accordingly, the MBMS data and the unicast data cannot be distinguishedand interference occurs. This degrades the transmission characteristicsof one or both of the MBMS data and the unicast data, resulting indegradation in transmission quality.

SUMMARY

According to an aspect of the invention, a radio communication systemincludes: a first radio station which performs communication by the useof a first radio signal; a second radio station; and a third radiostation which is in an area common to a radio communication area of thefirst radio station and a radio communication area of the second radiostation, wherein: the second radio station includes a processor which isconfigured for converting, upon receiving a second radio signal which isa scrambled radio signal and is indistinguishable from the first radiosignal, a communication format of the second radio signal; and theprocessor is configured for generating a third radio signal byconverting a communication format of a scrambled radio signal which isbased on the second radio signal and is distinguishable from the firstradio signal, and for communicating with the third radio station by theuse of the third radio signal.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example of the structure of a radio communicationsystem;

FIG. 2 illustrates an example of the structure of a radio communicationsystem;

FIG. 3 illustrates an example of the structure of a radio communicationsystem;

FIG. 4 illustrates a MBSFN network;

FIG. 5 is a sequence diagram of operation in the MBSFN network;

FIG. 6 illustrates a radio communication system in a MBSFN network;

FIG. 7 illustrates the replacement of a CP;

FIG. 8 illustrates the structure of a radio communication system;

FIG. 9 illustrates the structure of a relay node;

FIG. 10 illustrates the structure of the relay node;

FIG. 11 illustrates the structure of a mobile station;

FIG. 12 illustrates the structure of a radio communication system;

FIG. 13 is a sequence diagram of operation;

FIG. 14 illustrates the structure of a radio communication system;

FIG. 15 illustrates the structure of a radio communication system;

FIG. 16 is a sequence diagram of operation;

FIG. 17 illustrates the structure of a radio communication system;

FIG. 18 is a sequence diagram of transmission of MBMS data before normalMBSFN transmission timing;

FIG. 19 illustrates the structure of a radio communication system;

FIG. 20 illustrates the format of radio data;

FIG. 21 illustrates data receiving and combining;

FIG. 22 illustrates cell extension;

FIG. 23 illustrates countermeasures for a dead spot;

FIG. 24 illustrates the problem of being unable to distinguish betweenunicast data and MBMS data; and

FIG. 25 illustrates the occurrence of interference caused by a timingdeviation.

DESCRIPTION OF EMBODIMENTS

Embodiments will now be described with reference to the accompanyingdrawings. FIG. 1 illustrates an example of the structure of a radiocommunication system. A radio communication system 1 includes a radiostation (first radio station) 1 r, a radio station (second radiostation) 2 r, and a radio station (third radio station) 3 r.

The radio station 1 r performs communication by the use of a radiosignal (first radio signal) d1. The radio station 2 r receives a radiosignal (second radio signal) d2 on which scrambling that cannot bedistinguished from the radio signal d1 is performed. The radio station 2r includes a communication format conversion unit 21. The radio station3 r is in a radio communication area (cell) of the radio station 1 r anda cell of the radio station 2 r.

Being unable to distinguish the radio signal d1 and the radio signal d2means being unable to distinguish a code for scrambling which isperformed on the radio signal d1 and a code for scrambling which isperformed on the radio signal d2.

When the communication format conversion unit 21 included in the radiostation 2 r receives the radio signal d2, the communication formatconversion unit 21 converts a communication format of the radio signald2 by performing scrambling which can be distinguished from the radiosignal d1 on the radio signal d2. By doing so, the communication formatconversion unit 21 generates a radio signal d2 a (third radio signal).The communication format conversion unit 21 communicates with the radiostation 3 r by the use of the radio signal d2 a.

The contents themselves of a service signal in the radio signal d2 a arethe same as those of a service signal in the radio signal d2. However,the communication format of the radio signal d2 is converted so that theradio signals d1 and d2 a can be distinguished.

As has been described, even if the radio signals d1 and d2 cannot bedistinguished, the communication format conversion unit 21 converts thecommunication format of the radio signal d2 to be distinguished from theradio signal d1. The communication format conversion unit 21communicates with the radio station 3 r by the use of the generateddistinguishable radio signal d2 a.

In order to make it possible to distinguish the radio signals d1 and d2,it is desirable that frames (or slots included in frames) transmittedfrom the first and second radio stations should be synchronized. Inaddition, different radio resources may be used for the radio signals d1and d2.

The radio signals d1 and d2 a can be distinguished, so they do notinterfere with each other. Therefore, receiving quality at the radiostation 3 r and radio transmission quality in the entire system can beimproved.

FIG. 2 illustrates an example of the structure of a radio communicationsystem. A radio communication system 1A includes a base station (firstbase station) 10-1, a base station (second base station) 10-2, a relaynode 20, and a mobile station 30.

The base station 10-1 performs communication by the use of a radiosignal (first radio signal) d1. The base station 10-2 transmits a radiosignal (second radio signal) d2 which cannot be distinguished from theradio signal d1. The relay node 20 includes a communication formatconversion unit 21 and relays the radio signal d2 transmitted from thebase station 10-2.

The communication format conversion unit 21 converts a communicationformat of the radio signal d2 to a communication format which can bedistinguished from the radio signal d1. That is to say, thecommunication format conversion unit 21 generates a radio signal d2 a inthe communication format after the conversion and communicates with themobile station 30 by the use of the radio signal d2 a.

If the relay node 20 relays the radio signal d2 received from the basestation 10-2 to the mobile station 30 without changing its communicationformat, the radio signals d1 and d2 cannot be distinguished.Accordingly, interference occurs.

With the radio communication system 1A, on the other hand, the relaynode 20 performs relay communication by converting the communicationformat of the radio signal d2 to a communication format which can bedistinguished from the radio signal d1 and by generating the radiosignal d2 a. As a result, the radio signals d1 and d2 a do not interferewith each other. Therefore, receiving quality at the mobile station 30and radio transmission quality in the entire system can be improved.

FIG. 3 illustrates an example of the structure of a radio communicationsystem. In a radio communication system 1-1 a radio signal d1 is anormal communication signal d1 and a radio signal d2 is a broadcastsignal d2. The structure of the radio communication system 1-1 is thesame as that of the radio communication system 1A illustrated in FIG. 2.

When a communication format conversion unit 21 receives the broadcastsignal d2, the communication format conversion unit 21 converts abroadcast format which is a communication format of the broadcast signald2 to a normal communication format which is a communication format ofthe normal communication signal d1, and relay-transmits the broadcastsignal d2 in the normal communication format.

A broadcast signal d2 a the communication format of which has beenconverted to the normal communication format is transmitted to a mobilestation 30. Even when the mobile station is in an environment in whichthe mobile station 30 can receive both the normal communication signald1 and the broadcast signal d2 a, the communication format (normalcommunication format) of the normal communication signal d1 is the sameas that of the broadcast signal d2 a (that is to say, there is aguarantee that radio signals in the same communication format can bedistinguished) and interference does not occur. Therefore, receivingquality at the mobile station 30 and radio transmission quality in theentire system can be improved.

In an example in which the radio communication system 1-1 is applied toMBMS, the structure of a system and operation will now be described.First the structure of an entire MBSFN network to which the radiocommunication system 1-1 is applied will be described.

FIG. 4 illustrates a MBSFN network. A MBSFN network 40 includes a MBMScontroller or MBMS control unit (hereinafter generically named “MBMScontroller”) 41 which is a MCE (Multi-Cell/Multicast CoordinationEntity), a MBMS GW (Gate Way) 42, BTSs (Base Transceiver Stations) 43 aand 43 b, and mobile stations 30-1 through 30-4.

A MBMS radio signal includes MBMS data and a control signal (hereinafterreferred to as a “MBMS control signal”) for receiving a MBMS. The MBMScontroller 41 controls MBMS transmission for transmitting the MBMScontrol signal to the MBMS GW 42 and the base transceiver stations 43 aand 43 b. The MBMS GW 42 transmits the MBMS data to the base transceiverstations 43 a and 43 b. The MBMS GW 42 stores and manages the MBMS dataand may be referred to as a MBMS data storage unit.

FIG. 5 is a sequence diagram of operation in the MBSFN network. The MBMScontroller 41 performs scheduling to determine MBMS data to betransmitted and its transmission method (such as a modulation scheme, acoding scheme, transmission timing, and a radio frequency to be used).The MBMS controller 41 then gives the MBMS GW 42 notice of informationregarding the modulation scheme, the coding scheme, and the likedetermined and a control signal generated on the basis of theinformation.

In addition, the MBMS controller 41 requests the MBMS GW 42 to transmitthe MBMS data to base transceiver stations. The MBMS GW 42 whichreceives the notice transmits the control signal (MCCH: MulticastControl Channel) and the MBMS data (MTCH: MBMS Traffic Channel) to thebase transceiver station. In addition, the MBMS GW 42 gives the basetransceiver station notice of control information, such as thetransmission timing and the radio frequency to be used, for MBSFNtransmission.

The base transceiver station which receives the notice of the controlinformation, the MBMS data, and the control signal performs MBSFNtransmission in accordance with the control information. A DF (Decodeand Forward) relay node (which performs processes such as demodulation,error correction decoding, and re-coding and re-modulation on a receivedradio signal and relays the resultant) which receives the MBSFNtransmission performs demodulation and decoding, error correction, andrecoding and remodulation and transmits MBMS data obtained to a mobilestation.

The MBMS data forms a MTCH which is a logical channel, is mapped to aMCH (Multicast Channel) which is a transport channel, and isradio-transmitted via a PMCH which is a radio channel. When the MBMSdata is transmitted, scrambling is performed on the basis of an ID(identifier) according to MBSFN area (see TS36.211).

The MBMS control signal is included in a MCCH which is a logicalchannel, is mapped to a MCH which is a transport channel, and isradio-transmitted via a PMCH which is a radio channel.

The MBMS controller 41 performs scheduling, such as resource assignmentand determination of a MCS (Modulation and Coding Scheme) and MBMS datatransmission timing, multiplexes a scheduling result on the MBMS controlsignal, and transmits it. The base transceiver stations 43 a and 43 bperform radio transmission on the basis of the scheduling result.

The above MCS (which may also be referred to as AMC (Adaptive Modulationand Coding)) means a modulation and coding scheme. With the MCS amodulation scheme or a coding rate is adaptively changed according toradio channel quality and is used. The MCS includes attributes such as amodulation scheme, a coding rate, and a transmission rate.

With MCS1, for example, a modulation scheme is QPSK (Quadrature PhaseShift Keying), a coding rate is 1/8, and a transmission rate is 1.891Mb/s. With MCS5 a modulation scheme is 16QAM (Quadrature AmplitudeModulation), a coding rate is 1/2, and a transmission rate is 15.221Mb/s. Usually an optimum MCS is selected according to the receivingstate of a mobile station.

The MBMS controller 41 selects one of a plurality of MCSs. One methodfor selecting a MCS is to select a MCS with a cell in which apropagation characteristic (propagation environment) is most undesirableas reference and to apply the same MCS selected in the whole of a MBSFNarea.

For example, if the determination that communication is performed on thebasis of MCS1 in a cell in which a propagation characteristic is mostundesirable is made, then MCS1 is applied in all the other cells in aMBSFN area (MCS1 is also applied in a cell in which a propagationcharacteristic is good). It is also possible to set a certain MCSregardless of a propagation environment.

The operation of a radio communication system in a MBSFN network willnow be described concretely. Hereinafter description will be given withunicast data as an example of a normal communication signal, a unicastcommunication format as an example of a normal communication format,MBMS data as an example of a broadcast signal, and a MBSFN communicationformat as an example of a broadcast format.

FIG. 6 illustrates a radio communication system in a MBSFN network. Aradio communication system 1 a includes a MBMS controller 41, a MBMS GW42, base transceiver stations 43 a through 43 c, a relay node 20, andmobile stations 30-1 through 30-4. The relay node 20 includes acommunication format conversion unit 21.

The base transceiver station 43 a transmits MBMS data in the MBSFNcommunication format to the mobile station 30-1 and the relay node 20.The base transceiver station 43 b transmits unicast data in the unicastcommunication format to the mobile station 30-3. The base transceiverstation 43 c transmits unicast data in the unicast communication formatto the mobile station 30-4.

When the communication format conversion unit 21 included in the relaynode 20 receives the MBMS data in the MBSFN communication format, thecommunication format conversion unit 21 converts the MBSFN communicationformat to the unicast communication format and transmits the MBMS datain the unicast communication format.

It is assumed that the mobile station 30-2 receives data relayed by therelay node 20 and that the mobile station 30-2 is in an area where themobile station 30-2 can also receive unicast data transmitted from thebase transceiver station 43 b.

If the relay node 20 relay-transmits the MBMS data in the MBSFNcommunication format to the mobile station 30-2 under these conditions,then the mobile station 30-2 receives both the MBMS data in the MBSFNcommunication format and the unicast data in the unicast communicationformat.

With the MBSFN communication format the MBMS data is transmitted via aradio channel PMCH. With the unicast communication format the unicastdata is transmitted via a radio channel PDSCH. However, there is noguarantee that a code for scrambling performed on a PMCH and a code forscrambling performed on a PDSCH can be distinguished. Accordingly, itmay be impossible to distinguish these codes. As a result, the MBMS datainterferes with the unicast data at the mobile station 30-2.

On the other hand, it is assumed that the relay node includes thecommunication format conversion unit 21. When the communication formatconversion unit 21 receives the MBMS data in the MBSFN communicationformat, the communication format conversion unit 21 changes thecommunication format of the MBMS data from the MBSFN communicationformat to the unicast communication format and relay-transmits the MBMSdata in the unicast communication format.

That is to say, the MBSFN communication format is converted to theunicast communication format (radio data format using an extended CP isconverted to a radio data format using a normal CP), so the MBMS datacan be transmitted not via a radio channel PMCH but via a radio channelPDSCH.

As a result, the MBMS data in the unicast communication formattransmitted from the relay node 20 does not interfere with the unicastdata in the unicast communication format transmitted from the basetransceiver station 43 b.

That is to say, the MBMS data and the unicast data are transmitted viaradio channels PDSCH, so there is a guarantee that the MBMS data and theunicast data can be distinguished. This can prevent interference.Accordingly, the mobile station 30-2 can sensitively receive the MBMSdata which is transmitted from the relay node 20 and which the mobilestation 30-2 originally wants to receive.

In the above description the communication format conversion unit 21changes the communication format of the MBMS data from the MBSFNcommunication format to the unicast communication format andrelay-transmits the MBMS data. By changing the communication format ofthe MBMS data from the MBSFN communication format to a single cell MBMScommunication format and relay-transmitting the MBMS data, however, theoccurrence of interference can also be prevented. A single cell MBMSwill now be described.

With a LTE system not only MBSFN transmission but also single cell MBMStransmission (term “single cell transmission” is used in TS36.300, butin this specification the term “single cell MBMS transmission” is usedfor differentiating it from unicast transmission) by which MBMS data istransmitted only to a specific cell is discussed.

With the MBSFN transmission MBMS data is transmitted to the whole of anarea which is a group of cells. With the single cell MBMS transmission,unlike the MBSFN transmission, MBMS data is transmitted only to aspecific cell. Accordingly, there is no need for a plurality of basetransceiver stations to transmit the same data at the same frequency atthe same timing. As a result, each base transceiver station performsscheduling.

Moreover, MBMS data is transmitted to one cell, so propagation distanceis short compared with the MBSFN transmission. As a result, CP lengthcan be made shorter. In other words, a normal CP used in the unicastcommunication can be used. This means that the unicast transmission canbe performed. That is to say, transmission can be performed by the useof a PDSCH which is a radio channel used in the unicast communication.

Therefore, when the communication format conversion unit 21 receives theMBMS data in the MBSFN communication format, the communication formatconversion unit 21 may convert the MBSFN communication format to theunicast communication format or a single cell MBMS communication format.By relay-transmitting the MBMS data in the unicast communication formator the single cell MBMS communication format, the occurrence ofinterference at the mobile station can be prevented.

Format conversion (replacement of a redundant portion (CP)) will now bedescribed. FIG. 7 illustrates the replacement of a CP. When thecommunication format conversion unit 21 converts the MBSFN communicationformat to the unicast communication format or the single cell MBMScommunication format, the communication format conversion unit 21performs data format conversion by replacing an extended CP with anormal CP.

By adding a short normal CP to received data, the amount of informationwhich can be transmitted can be increased by the use of an empty field(because (length of normal CP)<(length of extended CP) or transmissioncan be performed with a coding rate decreased and the number of paritybits increased. As a result, a transmission characteristic can beimproved (transmission may be performed with a coding rate unchanged and0's or 1's inserted into unused bits as padding characters).

The case where the unicast communication format is converted to theMBSFN communication format will now be described. FIG. 8 illustrates thestructure of a radio communication system. The structure of a radiocommunication system 1 a-0 is the same as that of the radiocommunication system 1 a illustrated in FIG. 6. In the case of FIG. 8,however, the unicast communication format is converted to the MBSFNcommunication format.

A base transceiver station 43 a transmits unicast data in the unicastcommunication format to a mobile station 30-1 and a relay node 20. Abase transceiver station 43 b transmits MBMS data in the MBSFNcommunication format to a mobile station 30-3. A base transceiverstation 43 c transmits MBMS data in the MBSFN communication format to amobile station 30-4.

When a communication format conversion unit 21 included in the relaynode 20 receives the unicast data in the unicast communication format,the communication format conversion unit 21 converts the unicastcommunication format to the MBSFN communication format and transmits theunicast data in the MBSFN communication format (radio data format usinga normal CP is converted to a radio data format using an extended CP).

As a result, the unicast data in the MBSFN communication formattransmitted from the relay node 20 does not interfere with the MBMS datain the MBSFN communication format transmitted from the base transceiverstation 43 b. A communication format conversion reverse to thatdescribed in FIG. 6 can also be made in this way.

The structure of the relay node 20 will now be described. Methods ofrelay by the relay node 20 are broadly divided into an AF (Amplify andForward) method and the DF method. With the AF method a relay nodereceives a radio signal transmitted from a base transceiver station or amobile station, amplifies the received radio signal, and transmits aradio signal obtained to a mobile station or a base transceiver station.

With the DF method, as described above, a relay node receives a radiosignal transmitted from a base transceiver station or a mobile station,performs an error correction process by demodulation and decoding,performs coding and modulation again, and transmits a signal obtained toa mobile station or a base transceiver station. The structure of therelay node 20 having the DF function will now be described.

FIGS. 9 and 10 illustrate the structure of the relay node 20. The relaynode 20 includes an antenna a1, a receiving unit 22 a-1, a demodulationand decoding unit 22 a-2, a radio channel quality informationacquisition unit 23 a, a scheduler 24 a, a channel setting unit 25 a, anuplink connection request signal extraction unit 26 a-1, an uplinkconnection request signal generation unit 26 a-2, an uplink transmissioncontrol signal generation unit 26 a-3, a channel quality measurementunit 27 a-1, a channel quality information generation unit 27 a-2, acoding and modulation unit 28 a-1, and a transmission unit 28 a-2.

In addition, the relay node 20 includes an antenna a2, a receiving unit22 b-1, a demodulation and decoding unit 22 b-2, a downlink transmissioncontrol signal extraction unit 23 b-1, a MBMS control signal extractionunit 23 b-2, a downlink control signal generation unit 23 b-3, a MBSFNtransmission control unit 23 b-4, a transmitted data buffer 24 b, acommunication format conversion unit 21, a coding and modulation unit 25b-1, and a transmission unit 25 b-2.

On the basis of a scheduling result, the receiving unit 22 a-1 and thedemodulation and decoding unit 22 a-2 receive an uplink radio signaltransmitted from a mobile station via the antenna a1, down-convert it,and demodulate and decode an uplink signal after the down-conversion.

The radio channel quality information collection unit 23 a collectsradio channel quality information (indicator of the quality of a radiochannel between the relay node and the mobile station) from the uplinksignal after the demodulation and decoding and transmits the radiochannel quality information to the scheduler 24 a.

The uplink connection request signal extraction unit 26 a-1 extracts anuplink connection request signal from the uplink signal after thedemodulation and decoding and transmits the uplink connection requestsignal to the channel setting unit 25 a. When the channel setting unit25 a receives the uplink connection request signal, the channel settingunit 25 a transmits uplink connection request signal generationinstructions on the basis of the scheduling result.

When the uplink connection request signal generation unit 26 a-2receives the uplink connection request signal generation instructions,the uplink connection request signal generation unit 26 a-2 generates anuplink connection request signal. The uplink transmission control signalgeneration unit 26 a-3 generates an uplink transmission control signalon the basis of the scheduling result.

The channel quality measurement unit 27 a-1 measures the quality of achannel between a base transceiver station and the relay node 20 andtransmits a measurement result to the channel quality informationgeneration unit 27 a-2. The channel quality information generation unit27 a-2 generates channel quality information on the basis of themeasurement result.

On the basis of the scheduling result, the coding and modulation unit 28a-1 and the transmission unit 28 a-2 code and modulate the uplinkconnection request signal, the uplink transmission control signal, andthe channel quality information, multiplex these signals on one another,up-convert a signal obtained, and transmit the signal to the basetransceiver station via the antenna a2.

On the basis of information regarding coding and modulation included ina downlink transmission control signal, the receiving unit 22 b-1 andthe demodulation and decoding unit 22 b-2 receive via the antenna a2 adownlink radio signal transmitted from the base transceiver station,down-convert it, and demodulate and decode a downlink signal after thedown-conversion. The downlink transmission control signal extractionunit 23 b-1 extracts the downlink transmission control signal from thedownlink signal and transmits it to the receiving unit 22 b-1 and thedemodulation and decoding unit 22 b-2.

The MBMS control signal extraction unit 23 b-2 extracts a MBMS controlsignal from the downlink signal and transmits it to the MBSFNtransmission control unit 23 b-4. The MBSFN transmission control unit 23b-4 sets MBSFN control in the scheduler 24 a.

The transmitted data buffer 24 b buffers the downlink signal and outputsdata on the basis of a scheduling result. The communication formatconversion unit 21 converts the communication format of the downlinksignal after the buffering (MBSFN→unicast, for example). The downlinkcontrol signal generation unit 23 b-3 generates a downlink controlsignal on the basis of the scheduling result.

On the basis of the scheduling result, the coding and modulation unit 25b-1 and the transmission unit 25 b-2 code and modulate the downlinkcontrol signal and the downlink signal after the communication formatconversion, up-convert them, and transmit them to the mobile station viathe antenna a1.

The structure of a mobile station will now be described. FIG. 11illustrates the structure of a mobile station. A mobile station 30includes an antenna a3 and a receiving unit 31. It is assumed that themobile station 30 is in an area where the mobile station 30 can receivea radio signal (first radio signal) d1 and a radio signal (second radiosignal) d2 which cannot be distinguished from the radio signal d1.

When the receiving unit 31 receives the radio signal d1, the receivingunit 31 performs a process for receiving the radio signal d1.Alternatively, a communication format of the radio signal d2 isconverted on the mobile station 30 side to a communication format whichcan be distinguished from the radio signal d1, and the receiving unit 31performs a process for receiving a radio signal d2 a in thecommunication format after the conversion.

Detailed operation in a radio communication system will now bedescribed. In a first embodiment operation performed at the time ofconverting the MBSFN communication format to the unicast communicationformat and performing relay transmission will be described. A relay nodeincluded in a radio communication system has a MBMS scheduling function.

FIG. 12 illustrates the structure of a radio communication system. Aradio communication system 1 a-1 includes a MBMS controller 41, a MBMSGW 42, base transceiver stations 43 a and 43 b, a relay node 20 a, andmobile stations 30-1 through 30-3. The relay node 20 a includes acommunication format conversion unit 21 and a scheduler 2 a.

The relay node 20 a originally includes a scheduler for unicastcommunication. However, the scheduler 2 a has not only a unicastcommunication scheduling function but also a MBMS scheduling function.

The base transceiver station 43 a transmits MBMS data in the MBSFNcommunication format to the mobile station 30-1 and the relay node 20 a.The base transceiver station 43 b transmits unicast data in the unicastcommunication format to the mobile station 30-3.

When the communication format conversion unit 21 included in the relaynode 20 a receives the MBMS data in the MBSFN communication format, thecommunication format conversion unit 21 converts the MBSFN communicationformat to the unicast communication format and transmits the MBMS datain the unicast communication format to the mobile station 30-2.

The mobile station 30-2 requests the MBMS controller 41 via the relaynode 20 a and the base transceiver station 43 a to relay MBSFNtransmission. The relay node 20 a which receives the request requeststhe MBMS controller 41 via the base transceiver station 43 a to relayMBSFN transmission and transmit MBMS control information managed by theMBMS controller 41 to the relay node 20 a.

FIG. 13 is a sequence diagram of operation. In FIG. 13, it is assumedthat a relay request from a mobile station is transmitted to at least aDF relay node, that the relay request is transmitted to a basetransceiver station via the DF relay node, and that the relay request istransmitted to a MBMS controller via the base transceiver station.

The MBMS controller which receives the relay request transmits MBSFNtransmission information (information indicative of the type oftransmitted MBMS data, the MBMS data which has already been transmitted,and the like) held by the MBMS controller to the DF relay node so thatthe DF relay node will change the communication format of received MBMSdata from the MBSFN communication format to the unicast communicationformat and so that the DF relay node will transmit the MBMS data to themobile station. In FIG. 13, the MBMS controller transmits the MBSFNtransmission information before scheduling. However, the MBMS controllermay transmit the MBSFN transmission information after scheduling.

In addition, the mobile station may transmit radio channel qualityinformation to the DF relay node after MBSFN transmission from the basetransceiver station to the DF relay node. Furthermore, it is necessarythat the DF relay node should give the mobile station notice of relaystart timing before unicast communication. MBMS data is transmitted tothe DF relay node by the MBSFN transmission.

On the basis of the radio channel quality information transmitted fromthe mobile station, the DF relay node which receives the MBMS datagenerates MBMS control information to be transmitted to the mobilestation by the use of at least one of MBMS control informationtransmitted from the MBMS controller and MBMS control informationincluded in the MBMS data transmitted from the base transceiver station.The DF relay node transmits the MBMS control information to the mobilestation as control information for unicast communication and thentransmits the MBMS data.

The MBMS controller which receives a request to transmit the MBMScontrol information transmits the MBMS control information including,for example, information regarding a service received by the mobilestation to the DF relay node via the base transceiver station. Controlinformation indicative of a part of service data which has already beenreceived by the mobile station can be taken as a concrete example of theMBMS control information regarding the service. This control informationis important in maintaining the continuity of the service.

On the basis of the above MBMS control information, the DF relay nodegenerates a MBMS control signal and generates a MCCH which is a logicalchannel. This MCCH is mapped to a MCH which is a transport channel, andis radio-transmitted via a PMCH which is a radio channel.

If MBMS control information is not transmitted from the MBMS controlleror if the DF relay node cannot generate a MBMS control signal (cannotgenerate a MCCH, for example), then the DF relay node informs the mobilestation that it cannot relay MBSFN transmission, and does not relayMBSFN transmission.

If the number of mobile stations which request MBSFN transmission relayis smaller or greater than a threshold set in advance, then the DF relaynode does not relay MBSFN transmission and informs the mobile stationsthat the DF relay node does not relay MBSFN transmission.

A mobile station which is informed that the DF relay node cannot relayMBSFN transmission performs hand-over to another relay node or the basetransceiver station. To be concrete, the mobile station measuresreceiving power from other relay nodes or the base transceiver stationand selects a relay node or the base transceiver station from whichreceiving power is the highest as a hand-over destination, and performshand-over to it.

On the basis of the channel quality (or an indicator of the quality) ofa downlink between the relay node 20 a and the mobile station 30-2transmitted from the mobile station 30-2, the scheduler 2 a included inthe relay node 20 a then performs scheduling in the same way that isused for transmitting unicast data between the relay node 20 a and themobile station 30-2. The scheduler 2 a determines radio resources fortransmitting MBMS data and a MBMS control signal and a modulationscheme.

The scheduler 2 a may equally perform scheduling of unicast data andrelayed MBMS data or preferentially perform scheduling of unicast dataor relayed MBMS data. In addition, the scheduler 2 a may performscheduling of unicast data communication and MBMS data communicationseparately.

As stated above, the relay node 20 a receives the MBMS controlinformation and performs scheduling. If the relay node 20 a can relayMBSFN transmission as a result of scheduling, then the relay node 20 ainforms the mobile station 30-2 which makes a request to relay MBSFNtransmission that the relay node 20 a can relay MBSFN transmission.

That is to say, the relay node 20 a uses control information for givingthe mobile station 30-2 notice that the relay node 20 a relays the MBMSdata in the unicast communication format. The mobile station 30-2 whichreceives the notice receives a downlink physical control channel(DPCCH). By doing so, the mobile station 30-2 extracts controlinformation (MCS and the like) for downlink unicast data communicationand receives a downlink radio channel PDSCH including the MBMS data inaccordance with the MBMS control information.

If the mobile station 30-2 which receives the PDSCH radio channel canreceive the MBMS data without errors, then the mobile station 30-2returns an ACK to the relay node 20 a. If the mobile station 30-2receives the MBMS data including errors, then the mobile station 30-2returns a NACK to the relay node 20 a (MBMS data relay method in whichan ACK or a NACK is not returned can be adopted).

A process performed for relaying MBMS data will now be described. Whenthe relay node 20 a receives MBMS data transmitted from the basetransceiver station 43 a, the relay node 20 a converts the received datamapped to a slot format using an extended CP to a slot format using anormal CP. The relay node 20 a then performs coding and modulation onthe data and transmits the data to the mobile station 30-2.

On the basis of a transmission control signal transmitted from the relaynode 20 a by the use of a DPCCH, the mobile station 30-2 sets ademodulation scheme and a decoding scheme. By receiving a PDSCH by whichunicast data is transmitted, the mobile station 30-2 receives the MBMSdata.

In the above description the mobile station 30-2 makes a request via therelay node 20 a to relay MBSFN transmission. As a result of hand-over,however, the base transceiver station or its upper radio channel controlstation may request the relay node 20 a to relay MBSFN transmission.

Furthermore, the relay node 20 a generates a MCCH. However, thefollowing method may be used. The relay node 20 a manages the MBMScontrol information. When the relay node 20 a transmits the MBMS data,the relay node 20 a informs the MBMS controller 41 of the MBMS controlinformation and the MBMS controller 41 generates a MCCH.

As has been described, the relay node 20 a relays MBMS data which itreceives to the mobile station 30-2 in the unicast communication format.As a result, it is possible to relay the MBMS data without causinginterference.

In addition, a radio data format using an extended CP is converted to aradio data format using a normal CP at communication format conversiontime. As a result, transmission can be performed with a coding ratedecreased and the number of parity bits increased. Therefore, atransmission characteristic or a transmission rate can be improved.

Moreover, on the basis of the quality of a downlink between the relaynode 20 a and the mobile station 30-2 transmitted from the mobilestation 30-2, scheduling is performed in the same way that is used fortransmitting unicast data between the relay node 20 a and the mobilestation 30-2. By doing so, an optimum transmission method can beselected. As a result, a transmission characteristic or a transmissionrate can be improved.

Operation for converting the MBSFN communication format to the singlecell MBMS communication format and performing relay transmission willnow be described as a second embodiment. FIG. 14 illustrates thestructure of a radio communication system. The structure of a radiocommunication system 1 a-2 is the same as that of the radiocommunication system 1 a-1 illustrated in FIG. 12. The radiocommunication system 1 a-2 differs from the radio communication system 1a-1 in that a communication format conversion unit 21 converts the MBSFNcommunication format to the single cell MBMS communication format.

A mobile station 30-2 makes a request to relay MBSFN transmission. Abase transceiver station 43 a requests a MBMS controller 41 to transmitMBMS control information to a relay node 20 a. This is the same with thefirst embodiment.

The MBMS controller 41 which is requested to transmit the MBMS controlinformation transmits the MBMS control information to the relay node 20a in response to the request. On the basis of the transmitted MBMScontrol information, the relay node 20 a generates a control signal andgenerates a MCCH which is a logical channel. The relay node 20 a mapsthis MCCH to a DL-SCH (Downlink Shared Channel) which is a transportchannel, and performs single cell MBMS transmission by the use of a PMCHwhich is a radio channel.

With single cell MBMS transmission a short CP can be used. This is thesame with unicast transmission. Accordingly, the relay node 20 areceives MBMS data transmitted from the base transceiver station 43 a bythe use of an extended CP, and performs demodulation and decoding. Afterthat, the relay node 20 a converts the format of the MBMS data to theformat using a normal CP, performs coding and modulation on the MBMSdata, and transmits the MBMS data to the mobile station 30-2. This isthe same with the first embodiment.

A third embodiment will now be described. In the third embodiment a basetransceiver station carries out a MBMS scheduling function. In addition,a plurality of relay nodes is installed.

FIG. 15 illustrates the structure of a radio communication system. Aradio communication system 1 a-3 includes a MBMS controller 41, a MBMSGW 42, base transceiver stations 43 a-1 and 43 b, a relay node RN, andmobile stations 30-1 through 30-3. The base transceiver station 43 a-1includes a MBMS scheduler 4.

AF relay nodes RN_(AF) and DF relay nodes RN_(DF) may mingle. The casewhere AF relay nodes RN_(AF) and DF relay nodes RN_(DF) mingle in a cellof the base transceiver station 43 a-1 or one DF relay node is in a cellof the base transceiver station 43 a-1 (FIG. 15 indicates a relay nodegroup in which AF relay nodes RN_(AF) and DF relay nodes RN_(DF) mingleas a relay node RN) and where the base transceiver station 43 a-1performs scheduling of communication between all the relay nodes and themobile station 30-2 will be described (AF relay node does not performdemodulation or decoding, so it does not carry out communication formatconversion).

FIG. 16 is a sequence diagram of operation. FIG. 16 is an example of aprocess performed in the case of centralized scheduling. In threerespects FIGS. 16 and 13 differ. Firstly, a mobile station transmitsinformation (radio channel quality information) indicative of thequality of a radio channel between a DF relay node and the mobilestation to a base transceiver station via the DF relay node. Secondly,the base transceiver station performs whole scheduling of communicationby all mobile stations including a mobile station under the control ofthe DF relay node and a mobile station which communicates directly withthe base transceiver station on the basis of the radio channel qualityinformation, information indicative of the quality of a radio channelbetween the base transceiver station and the mobile station whichcommunicates directly with the base transceiver station, and the like.The quality of the radio channel between the base transceiver stationand the mobile station which communicates directly with the basetransceiver station is measured by this mobile station. Thirdly, controlinformation regarding a MBSFN transmission relay method determined as aresult of the scheduling and MBMS data are transmitted to the mobilestation via the DF relay node.

The following method is also discussed as a method for schedulingcommunication between the relay node RN and the mobile station 30-2. Thebase transceiver station 43 a-1 performs whole scheduling ofcommunication by the relay node RN in the cell of the base transceiverstation 43 a-1.

The base transceiver station 43 a-1 performs in this way scheduling oftransmission and receiving by one or more relay nodes RN which are inthe cell of the base transceiver station 43 a-1 and which perform relay.This method is referred to as centralized scheduling in the sense that acentral base transceiver station performs scheduling.

In unicast transmission or single cell MBMS transmission informationindicative of the quality of a radio channel between the relay node RNand the mobile station 30-2 transmitted from the mobile station 30-2 tothe relay node RN is transmitted from the relay node RN to the basetransceiver station 43 a-1.

The base transceiver station 43 a-1 collects radio channel qualityinformation transmitted from DF relay nodes RN_(DF) and the mobilestation 30-1 with which the base transceiver station 43 a-1 directlycommunicates in the scheduler 4 and perform scheduling. The basetransceiver station 43 a-1 then transmits scheduling information to eachDF relay node RN_(DF) by the use of a radio channel.

A DF relay node RN_(DF) which receives the scheduling informationgenerates a control signal on the basis of MBMS control information andgenerates a MCCH which is a logical channel. The DF relay node RN_(DF)maps this MCCH to a MCH which is a transport channel, andradio-transmits the MCH by the use of a PMCH which is a radio channel.When the DF relay node RN_(DF) receives MBMS data, changes itscommunication format to the unicast communication format or the singlecell MBMS communication format, and transmits the MBMS data to themobile station 30-2.

A fourth embodiment will now be described. In the above descriptionMBSFN transmission is performed between the base transceiver station andthe relay node. In the fourth embodiment, however, unicast transmissionis performed between a base transceiver station and a relay node andMBSFN transmission is performed between the relay node and a mobilestation.

FIG. 17 illustrates the structure of a radio communication system. Aradio communication system 1 a-4 includes a MBMS controller 41, a MBMSGW 42, base transceiver stations 43 a-2, 43 b, and 43 c, a relay node 20b, and mobile stations 30-1 through 30-3.

The base transceiver station 43 c transmits unicast data in the unicastcommunication format to the mobile station 30-1. The base transceiverstation 43 b transmits MBMS data in the MBSFN communication format tothe mobile stations 30-2 and 30-3.

The base transceiver station 43 a-2 includes a communication formatconversion unit 21-1 and the relay node 20 b includes a communicationformat conversion unit 21-2. The communication format conversion unit21-1 included in the base transceiver station 43 a-2 converts the MBSFNcommunication format to the unicast communication format and transmitsMBMS data in the unicast communication format. The communication formatconversion unit 21-2 included in the relay node 20 b converts theunicast communication format to the MBSFN communication format andtransmits the MBMS data in the MBSFN communication format.

Operation will be described. When a relay of MBSFN transmission isrequested from the mobile station 30-2 to the relay node 20 b, the relaynode 20 b gives the base transceiver station 43 a-2 and the MBMScontroller 41 a notice of this request. The MBMS controller 41 whichreceives the notice gives the MBMS GW 42 instructions to transmit MBMSdata to be transmitted to the mobile station 30-2 and the relay node 20b for relay to the base transceiver station 43 a-2 (at least at a timecorresponding to a delay caused by a relay process performed by therelay node 20 b, for example) before normal MBSFN transmission timing.

The base transceiver station 43 a-2 receives the MBMS data and thecommunication format conversion unit 21-1 included in the basetransceiver station 43 a-2 converts the format including an extended CPused for normal MBSFN transmission to the format including a normal CP.The base transceiver station 43 a-2 transmits the MBMS data in theunicast communication format to the relay node 20 b.

The relay node 20 b receives the MBMS data in the unicast communicationformat and the communication format conversion unit 21-2 included in therelay node 20 b converts the format using a normal CP to the formatincluding an extended CP. The relay node 20 b transmits the MBMS data inthe MBSFN communication format to the mobile station 30-2.

As a result, it is possible to perform MBSFN transmission between thebase transceiver station 43 a-2 and the relay node 20 b withoutinterfering with communication between the base transceiver station 43 band the mobile station 30-2. In addition, the base transceiver station43 a-2 transmits the MBMS data before normal MBSFN transmission timing,so the mobile station 30-2 can receive and combine the MBMS datatransmitted via the relay node 20 b and the MBMS data transmitted fromthe base transceiver station 43 b.

FIG. 18 is a sequence diagram of transmission of MBMS data before normalMBSFN transmission timing.

(S1) The base transceiver station 43 a-2 transmits MBMS data in theunicast communication format to the relay node 20 b, for example, atleast at a time corresponding to a delay caused by a relay processperformed by the relay node 20 b (a time corresponding to a delay causedby a series of processes, that is to say, by a demodulation and decodingprocess and a coding and modulation process performed by the relay node20 b which is, for example, a DF relay node) before normal MBSFNtransmission timing.

(S2) The relay node 20 b performs the demodulation and decoding processand the coding and modulation process on the MBMS data.

(S3) The communication format conversion unit 21-2 included in the relaynode 20 b converts the unicast communication format to the MBSFNcommunication format and converts the format using a normal CP to theformat using an extended CP.

(S4) The relay node 20 b transmits the MBMS data in the MBSFNcommunication format to the mobile station 30-2.

(S5) The base transceiver station 43 b transmits the MBMS data in theMBSFN communication format to the mobile station 30-2.

(S6) The mobile station 30-2 receives and synthesizes the MBMS datatransmitted via the relay node 20 b and the MBMS data transmitted fromthe base transceiver station 43 b.

In the above sequence diagram the base transceiver station 43 a-2transmits MBMS data in the unicast communication format before normalMBSFN transmission timing and the relay node 20 b converts the unicastcommunication format to the MBSFN communication format. However, whenthe base transceiver station 43 a-2 transmits MBMS data in the MBSFNcommunication format before normal MBSFN transmission timing, the relaynode 20 b also converts the MBSFN communication format to the unicastcommunication format.

A modification of the above radio communication systems will now bedescribed. In the above description the format using an extended CP isused for MBSFN transmission for the purpose of making it easy to receiveMBSFN transmission from a remote base transceiver station and increasingthe number of pieces of MBMS data which can be received and synthesized,that is to say, for the purpose of making it possible to receive MBMSdata for which a propagation delay is long.

The fact that the use of an extended CP makes it possible to receiveMBMS data for which a propagation delay is long shows that the radius ofa cell can be increased. Accordingly, in the modification an extended CPis used for transmitting data which is not limited to MBMS data in acell that is wider than a cell in which a normal CP is used.

If a relay node is installed in a cell with a long radius in themodification, then the relay node performs communication by the use of anormal CP because the radius of a cell of the relay node is short forits use.

FIG. 19 illustrates the structure of a radio communication system. Aradio communication system 1 b includes a base transceiver station 43 a,a relay node 20 c, and mobile stations 30-1 and 30-2 (MBMS controller41, a MBMS GW 42, and the like are not illustrated). The relay node 20 cincludes a radio transmission and receiving unit 2 c-1 and acommunication format conversion unit 2 c-2.

A cell 51 is a cell of the base transceiver station 43 a and a cell 52is a relay area of the relay node 20 c. The relay node 20 c and themobile station 30-1 are within the cell 51. The mobile station 30-2 isoutside the cell 51 and is within the cell 52.

The radio transmission and receiving unit 2 c-1 performs a radiotransmission and receiving process with the base transceiver station 43a or the mobile station 30-2. When the communication format conversionunit 2 c-2 communicates with the base transceiver station 43 a, thecommunication format conversion unit 2 c-2 performs communication by theuse of a first radio data format using a first redundant portion(extended CP, for example). When the communication format conversionunit 2 c-2 communicates with the mobile station 30-2, the communicationformat conversion unit 2 c-2 performs communication by the use of asecond radio data format using a second redundant portion (normal CP,for example) that is shorter than the first redundant portion.

In downlink transmission the base transceiver station 43 a transmitsdata D1 in the format using an extended CP. When the relay node 20 creceives the data D1, the communication format conversion unit 2 c-2transmits data D2 the format of which is converted to the format using anormal CP to the mobile station 30-2.

In uplink transmission the mobile station 30-2 transmits data D2 in theformat using a normal CP to the relay node 20 c. When the relay node 20c receives the data D2, the communication format conversion unit 2 c-2generates data D1 by converting the format to the format using anextended CP, and transmits the data D1 to the base transceiver station43 a.

As a result, the mobile station 30-1 within the cell receives data inthe format using an extended CP, so the mobile station 30-1 receives andsynthesizes plural pieces of data. Accordingly, receiving quality can beimproved. In addition, the relay node 20 c relays data in the formatusing a normal CP to the mobile station 30-2, so transmission can beperformed with a coding rate decreased and the number of parity bitsincreased. Therefore, a transmission characteristic can be improved.

One example of a hardware configuration of a radio base station will bedescribed. A radio base station includes a radio interface, processor,memory, logical circuit, and wired interface. The radio interface is aninterface device that performs radio communications with a radioterminal or a relay node, and for example, includes an antenna. Theprocessor is a device that processes data, and for example, includes aCPU (Central Processing Unit) and DSP (Digital Signal Processor). Thememory is a device that stores data, and for example, includes a ROM(Read Only Memory) and RAM (Random Access Memory). The logical circuitis an electronic circuit that performs logical calculation, and forexample, includes LSI (Large Scale Integration) and FPGA(Field-Programming Gate Array). The wired interface is an interfacedevice that performs wired communications with another radio basestation connected to a network of mobile telephone system side(so-called backhaul network).

One example of a hardware configuration of a relay node will bedescribed. A relay node includes a radio interface, processor, memory,and logical circuit. The radio interface is an interface device thatperforms radio communications with a radio base station, radio terminal,or another relay node, and for example, includes an antenna. Theprocessor is a device that processes data, and for example, includes aCPU (Central Processing Unit) and DSP (Digital Signal Processor). Thememory is a device that stores data, and for example, includes a ROM(Read Only Memory) and RAM (Random Access Memory). The logical circuitis an electronic circuit that performs logical calculation, and forexample, includes LSI (Large Scale Integration) and FPGA(Field-Programming Gate Array).

A correspondence between the relay node illustrated in FIGS. 9 and 10and such hardware components is as follows. The radio interfacecorresponds to the antennas a1 and a2, for example. The processor,logical circuit, and memory correspond to the communication formatconversion unit 21, receiving unit 22 a-1, . . . , and transmission unit28 a-2, for example.

One example of a hardware configuration of a radio terminal will bedescribed. A radio terminal includes a radio interface, processor,memory, logical circuit, input interface, and output interface. Theradio interface is an interface device that performs radiocommunications with a radio base station or relay node, and for example,includes an antenna. The processor is a device that processes data, andfor example, includes a CPU (Central Processing Unit) and DSP (DigitalSignal Processor). The memory is a device that stores data, and forexample, includes a ROM (Read Only Memory) and RAM (Random AccessMemory). The logical circuit is an electronic circuit that performslogical calculation, and for example, includes LSI (Large ScaleIntegration) and FPGA (Field-Programming Gate Array). The inputinterface is a device for inputs, and for example, includes operationalbuttons and microphone. The output interface is a device for outputs,and for example, includes a display and speaker.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiments of the presentinvention have been described in detail, it should be understood thatvarious changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A radio communication system comprising: a first radio station whichperforms communication by the use of a first radio signal; a secondradio station; and a third radio station which is in an area common to aradio communication area of the first radio station and a radiocommunication area of the second radio station, wherein: the secondradio station includes a processor which is configured for converting,upon receiving a second radio signal which is a scrambled radio signaland is indistinguishable from the first radio signal, a communicationformat of the second radio signal; and the processor is configured forgenerating a third radio signal by converting a communication format ofa scrambled radio signal which is based on the second radio signal andis distinguishable from the first radio signal, and for communicatingwith the third radio station by the use of the third radio signal.
 2. Aradio communication system comprising: a first base station whichperforms communication by the use of a first radio signal; a second basestation which transmits a second radio signal which is a scrambled radiosignal and is distinguishable from the first radio signal; a relay nodewhich performs a relay process on the second radio signal; and a mobilestation which is within a radio communication area of the first basestation and a relay area of the relay node, wherein: the relay nodeincludes a processor which is configured for converting a communicationformat of the second radio signal; and the processor generates a thirdradio signal by converting a communication format of a scrambled radiosignal which is based on the second radio signal and is distinguishablefrom the first radio signal, and relay-communicates with the mobilestation by the use of the third radio signal.
 3. The radio communicationsystem according to claim 2, wherein when the processor converts thecommunication format of the second radio signal to a communicationformat of the first radio signal, the processor replaces a redundantportion added to the second radio signal with a redundant portion usedin the first radio signal and generates the third radio signal.
 4. Theradio communication system according to claim 2, wherein: the firstradio signal is a normal communication signal and the second radiosignal is a broadcast signal; and the processor converts a broadcastformat which is a communication format of the broadcast signal to anormal communication format which is a communication format of thenormal communication signal, and generates the broadcast signal in thenormal communication format as the third radio signal.
 5. The radiocommunication system according to claim 4, wherein the processorreplaces, at the time of converting the broadcast format to the normalcommunication format, a first redundant portion added to the broadcastsignal with a second redundant portion used in the normal communicationsignal, and transmits the broadcast signal to which the second redundantportion is added as the third radio signal.
 6. The radio communicationsystem according to claim 2, wherein: the first radio signal is abroadcast signal and the second radio signal is a normal communicationsignal; and the processor converts a normal communication format whichis a communication format of the normal communication signal to abroadcast format which is a communication format of the broadcastsignal, and generates the normal communication signal in the broadcastformat as the third radio signal.
 7. The radio communication systemaccording to claim 6, wherein the processor replaces, at the time ofconverting the normal communication format to the broadcast format, afirst redundant portion added to the normal communication signal with asecond redundant portion used in the broadcast signal, and transmits thenormal communication signal to which the second redundant portion isadded as the third radio signal.
 8. The radio communication systemaccording to claim 2, wherein: the first radio signal is unicast dataand the second radio signal is MBMS data; and the processor converts aMBSFN communication format which is a communication format of the MBMSdata to a unicast communication format which is a communication formatof the unicast data or a single cell MBMS communication format, andgenerates the MBMS data in the unicast communication format or thesingle cell MBMS communication format as the third radio signal.
 9. Theradio communication system according to claim 8, wherein the processorreplaces, at the time of converting the MBSFN communication format tothe unicast communication format or the single cell MBMS communicationformat, an extended CP which is a redundant portion added to data atMBSFN transmission time with a normal CP which is a redundant portionshorter than the extended CP, and transmits the MBMS data to which thenormal CP is added as the third radio signal.
 10. The radiocommunication system according to claim 2, wherein: the first radiosignal is MBMS data and the second radio signal is unicast data orsingle cell MBMS data; and the processor converts a unicastcommunication format which is a communication format of the unicast dataor a single cell MBMS communication format which is a communicationformat of the single cell MBMS data to a MBSFN communication formatwhich is a communication format of the MBMS data, and generates theunicast data or the single cell MBMS data in the MBSFN communicationformat as the third radio signal.
 11. The radio communication systemaccording to claim 10, wherein the processor replaces, at the time ofconverting the unicast communication format or the single cell MBMScommunication format to the MBSFN communication format, a normal CPwhich is a redundant portion added to data at unicast data or singlecell MBMS data transmission time with an extended CP which is aredundant portion longer than the normal CP, and transmits the unicastdata or the single cell MBMS data to which the extended CP is added asthe third radio signal.
 12. The radio communication system according toclaim 2, wherein the second base station transmits the second radiosignal to the relay node at a time corresponding to a delay caused bythe relay process performed by the relay node.
 13. A relay nodecomprising: a processor configured for receiving a first radio signal,and for converting a communication format of the first radio signal,wherein when a radio station is in an area where the radio station canreceive a second radio signal and the first radio signal which is ascrambled radio signal and is indistinguishable from the second radiosignal, the processor generates a third radio signal by converting acommunication format of a scrambled radio signal which is based on thefirst radio signal and is distinguishable from the second radio signal,and communicates with the radio station by the use of the third radiosignal.
 14. A mobile station comprising: an antenna; and a processorconfigured for performing a process for receiving a radio signalreceived via the antenna, wherein when the mobile station is in an areawhere the mobile station can receive a first radio signal and a secondradio signal which is a scrambled radio signal and is indistinguishablefrom the first radio signal, the processor performs a process forreceiving the first radio signal or performs a process for receiving thesecond radio signal in a converted communication format which isgenerated on a transceiver side and is distinguishable from the firstradio signal.
 15. A radio communication method comprising: performing,by a first base station, communication by the use of a first radiosignal; transmitting, by a second base station, a second radio signalwhich is a scrambled radio signal and is indistinguishable from thefirst radio signal is performed; performing, by a relay node, a relayprocess on the second radio signal, wherein a mobile station is within aradio communication area of the first base station and a relay area ofthe relay node, and the relay node includes a processor which isconfigured for converting a communication format of the second radiosignal; and generating, by the processor, a third radio signal byconverting a communication format of a scrambled radio signal which isbased on the second radio signal and is distinguishable from the firstradio signal, and communicating with a third radio station by the use ofthe third radio signal.
 16. A radio communication system comprising: abase station; a relay node which is within a radio communication area ofthe base station; and a mobile station which is within a relay area ofthe relay node, wherein: communication is performed between the basestation and the relay node in a first radio format using a firstredundant portion; and communication is performed between the relay nodeand the mobile station in a second radio format using a second redundantportion shorter than the first redundant portion.
 17. A radio apparatusfor communicating with a first radio station and a second radio station,the apparatus comprising: a processor configured for performing atransmission and receiving process with the first radio station and thesecond radio station, for performing, at the time of communicating withthe first radio station, communication by the use of a first radioformat using a first redundant portion and for performing, at the timeof communicating with the second radio station, communication by the useof a second radio format using a second redundant portion shorter thanthe first redundant portion.